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d94e6fe0fd
Use the compiler intrinsic __builtin_popcount. Change-Id: I58286fbcf66d1068390ea9caff2f98b8fe244c2d Reviewed-on: https://go-review.googlesource.com/16831 Reviewed-by: Andrew Gerrand <adg@golang.org>
34 lines
927 B
Go
34 lines
927 B
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// +build !amd64 appengine
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// +build !gccgo
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package intsets
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import "runtime"
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// We compared three algorithms---Hacker's Delight, table lookup,
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// and AMD64's SSE4.1 hardware POPCNT---on a 2.67GHz Xeon X5550.
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//
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// % GOARCH=amd64 go test -run=NONE -bench=Popcount
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// POPCNT 5.12 ns/op
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// Table 8.53 ns/op
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// HackersDelight 9.96 ns/op
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//
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// % GOARCH=386 go test -run=NONE -bench=Popcount
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// Table 10.4 ns/op
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// HackersDelight 5.23 ns/op
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//
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// (AMD64's ABM1 hardware supports ntz and nlz too,
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// but they aren't critical.)
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// popcount returns the population count (number of set bits) of x.
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func popcount(x word) int {
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if runtime.GOARCH == "386" {
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return popcountHD(uint32(x))
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}
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return popcountTable(x)
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}
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